Many can bodies for food, beverages or other products are provided with easy open can ends that are characterized by having a pull tab attached to the can end which is used to fracture a tear panel on the can end defined by a score line on the can end. The pull tab may be lifted to depress the tear panel in order to provide an opening in the can end for dispensing the contents of the container.
Likewise, many food products are sold in can bodies provided with full open easy open can ends that are characterized by having a pull tab attached to the can end which is used to fracture a score line that circumscribes the circumference of the end panel to define an opening panel. The pull tab may be lifted to fracture the score line. After the score line is fractured, the pull tab may be pulled upward from the container which severs the remainder of the score line in order to remove the entire opening panel for dispensing the contents of the container.
In the manufacture of an easy open can end, a shell is conveyed to a conversion press. In the industry, a pre-converted can end is commonly referred to as a shell. In the typical operation of a conversion press, a shell is introduced between an upper tool member and a lower tool member, which are in the open, spaced apart position. A press ram advances the upper tool member toward the lower tool member in order to perform any of a variety of tooling operations such as rivet forming, paneling, scoring, embossing, and final staking. After performing a tooling operation, the press ram retracts until the upper tool member and lower tool member are once again in the open, spaced apart position. The partially converted shell is transported to the next successive tooling operation until an easy open can end is completely formed and discharged from the press. As one shell leaves a given tooling operation, another shell is introduced to the vacated operation, thus continuously repeating the entire easy open can end manufacturing process. Examples of easy open can ends can be found in U.S. Pat. Nos. 4,465,204 and 4,530,631. Conversion presses can operate at speeds that manufacture in excess of 500 can ends per minute per lane, with certain presses having four lanes of tooling manufacturing in excess of 2000 converted can ends per minute.
It has been the practice in the industry to continue to strive to reduce the starting gauge of the metal sheet stock used to form the can end. The current practice is to use metal with a starting gauge of approximately 0.008 inch (0.20 mm). As such, tooling stations in a conversion press must be rigorously maintained within prescribed operating tolerances due to the thin sheet stock used in the press. In the production of a converted can end in a conversion press, the scoring station is of particular concern. The scoring station employs a tooling member that has a knife edge which defines the tear panel or opening panel on the public side of the can end.
Steel sheet stock used in the manufacture of can ends has a coating which protects the metal by inhibiting oxidation, corrosion or rust from forming on the surface of the metal. During the conversion process, damage to the protective coating typically occurs while forming the score that defines the tear panel or opening panel of the can end. As noted above, in the conversion of a shell into a can end with openable features thereon, a score line is formed. This score line defines the tear panel or opening panel described above. The score line is the most likely location where damage is caused to the pre-conversion, protective coating. Any oxidation, corrosion or rust on the surface of the can end represents an unattractive product appearance to the consumer and is unacceptable to canmakers in general.
In the industry, as a precautionary measure to prevent oxidation, corrosion or rust from appearing on the can end, many canmakers apply a mixed solution to the scored area of the can end by spraying the can end. The accepted spraying apparatus and method in the industry for score repair on full open easy open ends utilizes a single holding tank that holds a plurality of components (e.g., solvent and epoxy) that are flowed through a fluid delivery system and a spray apparatus for applying the mixed solution to the can end.
These score repair machines use many different variations of two or more component epoxy mixtures for the application of mixed solution to the score lines of the can end. The fluid delivery systems require routine maintenance because the two or more component mixed solution has a finite tank life when mixed and need to be cleaned or purged from the machine when the mixed solution expires. The existing fluid delivery systems pump mixed solution and the mixed solution wets many of the pumping components and auxiliary components including, by way of example and not limitation, filters, valves, pumps, pressure transducers and check valves, etc. The mixed solution has a negative effect on the overall efficiency of many components of the machine because so many components are wetted with the mixed solution and require cleaning when the mixed solution expires.
Conversely, the mixing apparatus and method of the present invention will mix the components of the mixed solution on demand. The apparatus also contains a pressure tank that eliminates the exposure of the mixed solution to the pumping components and auxiliary components used in the fluid delivery system which simplifies cleaning and maintenance of the fluid delivery system. The apparatus of the present invention does not have any high pressure pumps or repair fluid pressure regulators that contact the mixed solution and can be designed for low pressure spray devices or high pressure spray devices. The apparatus also provides the end-user with greater flexibility by being able to use different mixing ratios of the base components (e.g., 4:1—solvent:epoxy, or any other combination.) The apparatus also allows the holding tanks to be continuously replenished with liquids or fluids while the mixing apparatus is operating because the liquids or fluids are drawn from storage tanks at atmosphere.
There continues to be a need in the art for a mixing apparatus and method of the present invention that mixes components of a mixed solution on demand. Also, there continues to be a need in the art for a mixing apparatus and method of the present invention that uses a pressure tank that eliminates the exposure of the mixed solution to the pumping components and auxiliary components used in the system in order to simplify cleaning and maintenance of the fluid delivery system. Additionally, there continues to be a need in the art for a mixing apparatus and method of the present invention that can accommodate different mixing ratios of the components of the mixed solution. Also, there continues to be a need in the art for a mixing apparatus and method of the present invention that allows holding tanks to be continuously replenished with liquids or fluids while the mixing apparatus is operating.